Quick sort implementation in Python

quick_sort.py

"""Implement quick sort in Python.
Input a list.
Output a sorted list."""
def sort_slice(list_slice):
    # pivot location always starts on the right
    end_idx = len(list_slice) - 1
    pivot_idx = end_idx
    # compare location always starts on the left
    compare_idx = 0
    while(True):
        pivot_value = list_slice[pivot_idx]
        compare_value = list_slice[compare_idx]
        
        # If the pivot location starts out the same of the compare location then
        # sorting is completely done for this slice and can be returned
        if (pivot_idx == 0):
            return list_slice
            
        # If pivot is less than comparison, shift the pivot to the left
        if (pivot_value < compare_value):
            list_slice[compare_idx] = list_slice[pivot_idx - 1]
            list_slice[pivot_idx - 1] = list_slice[pivot_idx]
            list_slice[pivot_idx] = compare_value
            pivot_idx -= 1
        # If pivot is greater than the comparison, shift the comparison to the right
        elif (pivot_value > compare_value):
            compare_idx += 1
        # Pivot is determined, now we need to recursively sort left and right sides
        else:
            left_slice = sort_slice(list_slice[0:pivot_idx])
            right_slice = []
            if (pivot_idx < end_idx):
                right_slice = sort_slice(list_slice[pivot_idx+1:])

            # Finally, return the concatenated parts of the sorted list
            return left_slice + [pivot_value] + right_slice
        
    return None